A turbocharger may be used to increase the power output of an internal combustion engine. The turbocharger does so by pressurizing the intake air, thereby increasing the mass of air provided to each of the engine's combustion chambers during the intake stroke. The increased air mass supports combustion of a correspondingly greater amount of fuel delivered to each combustion chamber, which provides increased power relative to a naturally aspirated engine of similar displacement. In a motor vehicle, a turbocharged engine may provide increased fuel economy by maintaining a higher power-to-weight ratio than a naturally aspirated engine of similar output and recovering internal energy from the exhaust to drive the turbocharger compressor. A turbocharger may be advantageously matched to an engine by creating an ‘operating net,’ defining appropriate pressure and flow conditions for the turbocharger compressor between surge and choked flow lines. Proper sizing of the operating net is required to meet the attributes of the engine: making the operating net too large may result in poor response and emissions characteristics, for example.
However, a turbocharger compressor coupled to an internal combustion engine may be subject to unwanted surge when a pressure ratio in the turbocharger compressor (viz., P, the ratio of the outlet pressure to the inlet pressure) is too great relative to the flow of air through the turbocharger compressor. Turbocharger compressor surge (TCS) is a dynamic instability mode that can generate air-flow and pressure oscillations of great amplitude; this condition may induce undesirable stresses in the turbocharger and the intake, including excessive torsional loading on the turbocharger shaft. Continued or excessive TCS may decrease the longevity of the turbocharger and/or the engine to which it is coupled. Further, TCS in a motor vehicle may adversely affect motorist satisfaction by causing undesirable vibration, noise and power loss. Turbocharged engine systems may therefore be configured to detect certain kinds of TCS and to take action to suppress TCS when it is detected.
For example, a turbocharged engine system may be configured to sense a pressure ratio P and a mass flow rate M of air into the engine intake, and to indicate TCS if the value of P lies outside an interval determined for the value of M. The converse is also possible—indicating TCS if the value of M lies outside an interval determined for the value of P. However, such approaches may not be the most suitable for all types of TCS.
The pressure-ratio and mass-flow rate intervals referenced above may be determined based on steady-state conditions of the engine, where engine speed and load are related predictably to each other. Under such conditions, calculations may be used to predict, for any value of M, the appropriate P interval below which TCS will not occur. But TCS may also occur during transient states of the engine, where speed and load are not related to pressure ratio and mass-flow rate as they are under steady-state conditions. Such transient states include, for example, tip-out, rich combustion (intake throttle closed relative to steady state), and exhaust-gas recirculation (intake throttle open relative to steady state). Under these conditions and others, methods of TCS detection based on steady-state P or M intervals may not appropriately detect TCS.
To address this issue, some engine systems use P or M intervals derived from steady-state calculations, but build in wide safety margins (e.g., 20%) to guard against transient TCS. This approach, however, may significantly limit turbocharger performance and may undermine the advantages of the turbocharged engine system.
The inventors herein have recognized the inadequacies of the existing methods outlined above and have provided various approaches directed to transient TCS response. In one embodiment, a method for responding to an existing or incipient surge condition of a turbocharger coupled to an engine of a motor vehicle is provided. The method comprises receiving a signal responsive to an operating condition of the turbocharger and adjusting one or more operating parameters of the motor vehicle when a power of the signal, integrated over a pre-selected range of non-zero frequencies, exceeds a pre-selected threshold. Other embodiments provide related systems for responding to an existing or incipient surge condition of a turbocharger. The systems and methods disclosed herein provide a reliable response to transient TCS whilst avoiding excessive constraints on turbocharger performance.
It will be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description, which follows. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined by the claims that follow the detailed description. Further, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.